Many types of cancer are thought to begin as the results of alterations in one's genes. One of these genes, ras, plays an important role in the development of many types of cancers. In order for the ras protein to function, a molecular group (called a "farnesyl" group) must be added to it. If one can prevent this "farnesyl" group from being added, the theory goes, one can prevent the abnormal ras form working and one can keep the cancer form growing and spreading. SCH 66336 is a dry which prevents the asditionaof farnesyl groups to certain proteins. While it has been found to shrink tumors in mice, we cannot be sure of the precise mechanism of action.